This invention relates to a method for depositing material on a depression, more particularly, relates to a method in which a photo CVD process is carried out so that the deposition is effectively performed also on insides of depressions.
There are broadly known and used a low pressure CVD, a plasma CVD as chemical vapor deposition method for semiconductor processing. In the semiconductor processing, depressions such as a hole, a trench, a cave (a sub-surface re-entrant opening having surfaces out of line-of-sight) or so on are configured on whose surfaces are placed product of the CVD method to form a buried field insulating layer or an electric element such as a capacitance in the depression, or to fill an over-etching region in the form of a depression. When a formation of layer on the depression is desired, it is inevitable that the thickness of the layer on a inner surface ( depression ) "ds" and the thickness of the layer on a upper surface "dt" result in ds/dt&gt;1. One of the problems of researching to obtain a finely configured semiconductor in VLSI field is how dt/ds can be increased near 1. Further, in case where the depth of a cave has a measure more than the measure of the opening of the cave, it was impossible to form a uniform layer throughout the inside of the cave. Such caves is formed, e.g., with a known trench method which can dig a cave of depth having a measure 3 to 5 times as large as the measure of the width of the opening thereof. Anyhow, existing methods are not suitable to perform a deposition in such a cave.
Namely, according to an existing CVD method, atoms or molecules are deposited on a substrate under exited condition which are diffused into vapor after decomposed or undergoing a reaction caused by thermal energy. The existing process can be performed effectively when it is carried out under negative pressure, since the active molecules have a relatively long mean free path in the vapor under a negative pressure, compared with that under the atmospheric pressure. For example, on a substrate with a trench of 2 micron meters in width and also in depth, a depression resulted in a layer 1 of micron meter thickness on the upper surface, a layer with at most thickness of 0.7 micron meter on the side wall of the trench and a layer with the thickness of 0.6 micron meter on the bottom of the trench. In any case, a step coverage ds/dt is expected only up to about 0.7.
According to other known method, step coverages are no more than that of the above method. Normaly, ds/dt=0.3-0.5. A plasma enhanced CVD alone is comparable with the above LPCVD.